1. Field of the Invention
The present invention relates to multiwavelength imaging and a spectroscopic photoemission microscope system. In particular, the present invention relates to a multiwavelength imaging and spectroscopic photoemission microscope system which may simultaneously provide images in a broad range of the electromagnetic spectrum, such as between 200 nm-1000 nm (ultraviolet and visible light) and 1000 nm-2500 nm (infrared light). The present invention may be used in failure analysis of integrated circuits and in semiconductor and low temperature physics.
2. Discussion of Related Art
It is known that certain physical phenomena, occurring within microdevices such as semiconductor devices, contribute to degradation of the device's performance under various operating conditions. Such phenomena are known to occur, for example, within insulatedgate field-effect transistors (IGFETs), metal oxide semiconductor field-effect transistors (MOSFETs), and virtually all semiconductor devices containing p-n junctions.
One type of phenomena which may contribute to degradation in the performance of MOSFETs is the emission of hot electrons from the MOSFET's silicon substrate into the gate insulator layer under various bias conditions. See generally, P. Correll, R. Troutman, and T. Ning, "Hot-Electron Emission in N-Channel IGFET's", IEEE Trans. on Electron Devices, Vol. ED-26, pp. 520-33 (1979). It is believed that the resulting substrate current may, in turn, overload the substrate-bias voltage, causing substrate potential fluctuations or electron injection into the substrate, inducing snap-back breakdown and CMOS latchup. Another type of phenomena causing degradation in MOSFET performance is believed to be caused by electron trapping in the oxide. Id.
It is known that certain physical phenomena contribute to breakdown across a p-n junction upon the application of a forward or reverse bias. See generally, A. Chynoweth and K. McKay, "Photon Emission from Avalanche Breakdown in Silicon", Phys. Rev., Vol. 102, pp. 369-76 (1956). In many cases, such breakdown is undesirable.
The occurrence of these and other undesirable physical phenomena within semiconductor devices are known to be accompanied by the emission of electromagnetic radiation. For example, photon emission spectrum characteristics resulting from latchup and hot electrons in n-channel MOSFETs have been measured in the visible spectrum. See, e.g., T. Aoki and A. Yoshii, "Analysis of Latchup-Induced Photoemission", IEDM Technical Digest 89-281, pp. 281-84 (1989). Moreover, emission spectrum characteristics from forward and reversed biased p-n junction diodes have also been measured in the visible spectrum. See, A. Chynoweth and K. McKay, "Photon Emission from Avalanche Breakdown in Silicon", Phys. Rev., Vol. 102, pp. 369-76 (1956). These emissions are believed to be generated by Bremsstrahlung radiation, i.e, broad band radiation emission when an energetic electron is decelerated in an electric field.
It is highly desirable to measure the electromagnetic radiation emitted from semiconductors to determine whether the aforementioned and other undesirable phenomena contributing to degradation of performance are occurring or may occur under certain operating conditions. It is also desirable to locate spatially from within the microdevice where the radiation is emitted. Detections of such radiation emission, by measuring the "thermal signature" of the device, can form the basis for testing failure mechanisms in semiconductor devices, and can be used to detect defects in individual semiconductors or locate problems in various manufacturing processes. Moreover, such measurement can be utilized to predict failures in semiconductors and to improve overall design.
Most failures of semiconductor devices will be accompanied by abnormal thermal signatures, e.g., some devices might become very hot while some might never turn on when powered up. The change in thermal signature due to the failure mechanism, however, may be difficult to view, due to operating temperature, small thermal gradient, or small device size.
In the past, measurements of such electromagnetic radiation emissions from semiconductors have been performed in the optical spectrum. This basic technology has now evolved into photoemission microscopy and is being used in industry in testing failure mechanisms in semiconductor devices.
It is desirable, however, to measure radiation emissions in other wavelengths of the electromagnetic spectrum. This provides a more complete spectral analysis of the emitted radiation and thermal signatures in semiconductor devices that result from failure mechanisms, thus providing additional test data. Moreover, certain undesirable phenomena produce infrared radiation, but do not generate radiation in the visible spectrum. Therefore, detection of such phenomena cannot be accomplished using measurements limited solely to the visible spectrum.
The device described in the '830 patent is configured to detect infrared radiation only. It is desirable, however, to detect simultaneously a wide band of electromagnetic energy emitted by an IC device in the visible and infrared spectra.
Therefore, it is an object of the present invention to provide a spectroscopic and photometric imaging photoemission microscope which images a wide band of energy wavelengths, such as the visible spectrum to the infrared spectrum.